Arguments

For the "formula" method, x should be a formula of the
form ~ x | g1 * g2 * ..., where x should be a
numeric variable. For the "numeric" method, x should
be a numeric vector.

data

For the formula method, an optional data source (usually a
data frame) in which variables are to be evaluated (see
xyplot for details). data should not be
specified for the other methods, and is ignored with a warning if it
is.

distribution

A quantile function that takes a vector of probabilities as argument
and produces the corresponding quantiles from a theoretical
distribution. Possible values are qnorm,
qunif, etc. Distributions with other required
arguments need to be provided as user-defined functions (see example
with qt).

f.value

An optional numeric vector of probabilities, quantiles corresponding
to which should be plotted. This can also be a function of a single
integer (representing sample size) that returns such a numeric
vector. A typical value for this argument is the function
ppoints, which is also the S-PLUS default. If specified, the
probabilities generated by this function is used for the plotted
quantiles, through the quantile function for the
sample, and the function specified as the distribution
argument for the theoretical distribution.

f.value defaults to NULL, which has the effect of
using ppoints for the quantiles of the theoretical
distribution, but the exact data values for the sample. This is
similar to what happens for qqnorm, but different from the
S-PLUS default of f.value=ppoints.

For large x, this argument can be used to restrict the number
of points plotted. See also the tails.n argument in
panel.qqmath.

panel

A function, called once for each panel, that uses the packet (subset
of panel variables) corresponding to the panel to create a display.
The default panel function panel.qqmath is documented
separately, and has arguments that can be used to customize its
output in various ways. Such arguments can usually be directly
supplied to the high-level function.

Further arguments. See corresponding entry in xyplot
for non-trivial details.

Details

qqmath produces Q-Q plots of the given sample against a
theoretical distribution. The default behaviour of qqmath is
different from the corresponding S-PLUS function, but is similar to
qqnorm. See the entry for f.value for specifics.

The implementation details are also different from S-PLUS. In
particular, all the important calculations are done by the panel (and
prepanel function) and not qqmath itself. In fact, both the
arguments distribution and f.value are passed unchanged
to the panel and prepanel function. This allows, among other things,
display of grouped Q-Q plots, which are often useful. See the help
page for panel.qqmath for further details.

This and all other high level Trellis functions have several arguments
in common. These are extensively documented only in the help page for
xyplot, which should be consulted to learn more detailed
usage.

Value

An object of class "trellis". The
update method can be used to
update components of the object and the
print method (usually called by
default) will plot it on an appropriate plotting device.